1. Field of the Invention:
This invention relates to valve apparatus, and, more particularly, to shutoff valve apparatus in which a piston is movable in a bore and the piston is spring-biased to a closed position and the piston includes a passage through which fluid flows.
2. Description of the Prior Art:
U.S. Pat. No. 455,853 (Shepard) discloses a pressure relief valve in which a spring-biased piston includes a plurality of apertures extending through a piston skirt. As pressure against the piston increases beyond a predetermind level, according to the rate of the springs, the piston moves and the apertures in its skirt allow pressure to be vented.
U.S. Pat. No. 2,731,981 (Glasser) discloses a pressure relief valve using a spring-biased piston. The piston includes a conically tapered surface, and there is a matching conically tapered valve seat. The piston includes passages extending through the piston. When pressure increases above a predetermined level, the valve opens and pressure is vented through the piston passages.
U.S. Pat. No. 2,886,058 (Horton) discloses two embodiments of check valves. Both embodiments utilize spring-biased pistons with spherical heads. The spherical heads extend into mating seats. Adjacent to the spherical heads there are a plurality of passages extending through the pistons. Both pistons work on the same principle. As excess pressure builds against the spherical heads, the pistons move, and pressure is vented through the passages.
U.S. Pat. No. 2,977,980 (Scholin) discloses a rather complicated valve for a metering pump. The apparatus includes a movable valve stem and a cavity which receives the valve stem and which holds a predetermined amount of fluid. As the valve stem moves into the cavity, the fluid is forced against a check valve which in turn moves under the hydraulic force to allow the predetermined volume of fluid to flow out of the apparatus. Back pressure against the check valve causes the check valve to move to prevent further flow. The check valve includes two separate passage systems, one through which the initial fluid flows, and a second through which the fluid flows out of the check valve. Two different types of pressure are used to help seat the check valve. One type of spring pressure is from a helically configured spring, and the second type of spring pressure is from a resilient, cylindrical sleeve.
U.S. Pat. No. 3,943,969 (Rubin et al) discloses a check valve which includes a spring-biased piston, and the piston includes a skirt with a plurality of apertures extending through the skirt. An O-ring is disposed about one end of the piston and the O-ring seats against a valve seat. The valve seat is simply a flat shoulder adjacent to a bore in which a portion of the piston extends. The bore comprises a guide for the movement of the piston. A spring biases the piston against the flow of fluid. Relatively low back pressure acts with the spring to urge the O-ring to seat against the shoulder to prevent fluid flow. However, since there is nothing to restrict the radially outwardly expansion of the O-ring, the O-ring may distort under sufficient back pressure and thus allow fluid to escape. The O-ring seal is not in a traditional O-ring seal environment and thus problems may occur.